If you clip a healthy plant without asking the owner first, you're a dick. But if I see you do it at a store, no I didn't. Cause the store made $2,550,000 while I was typing this.
It's not theft, it's basically dumpster diving for living things. Living things that can grow in dirt with some water.
They just see lost profit not an actual product loss.
My father enjoys grafting plants, he has an apple tree with 15 types of apples on it. Come to find out he's been snipping tiny branches off apple trees at Home Depot....
Maybe it is illegal in the sense that some succulents ARE invasive species
I do know that people go to garden shops looking for free material for growth lying on the ground, which id argue is unnecessary. Most people who own plants or a garden will happily share with you the fact if you show the ittyest bittiest piece of interest in them, and also share plants as well.
Hell I regularly give out succulent saplings for free or as a gift to friends and people I meet.